Stream depletion rate and volume from groundwater pumping in wedge-shape aquifers

Abstract

In river basins with several tributaries, wells in alluvial valleys are often located near the wedge-shaped confluence of two tributaries. Therefore, stream depletion characteristics, namely stream depletion rate (SDR) and stream depletion volume (SDV), induced by the pumping wells are distributed between two tributaries upstream from the confluence. Existing methods for the evaluation of stream depletion characteristics are applicable only for a wedge-shaped aquifer with special or uncommon wedge angles or for steady-state conditions. In water resources management, temporal stream depletion characteristics are important for the adjudication of water rights. A new and practically important method for analytical evaluation of transient SDR and SDV is developed for a wedge-shaped aquifer with arbitrary wedge angles. Results are obtained for each of two tributaries or the tributary segment lengths. A simple expression for the SDR fraction that originates from each tributary is presented for long period of pumping after which 100% of the pumping rate is supplied by stream depletion. The sensitivity analyses for different parameters are performed to examine their affects on the influence period of the total SDR and the results indicated that the SDR is sensitive to the angles of wedge-shaped aquifer and the pumping well. The results and sensitivity analysis presented in this study may provide useful information in the assessment of water balance or exploitation of river basins.